The present invention relates to a vacuum evacuation system for producing high vacuum in a system to be evacuated and, more particularly, to a vacuum evacuation system suitable for semiconductor manufacturing apparatuses.
As disclosed, for example, in "Shinkuu Gijutu Jitsumu Tokuhon (Vacuum Technique Practice Reader)" written by Katsuya Nakayama, published on Oct. 25, 1967, Ohm-Sha, pages 21-22, the conventional vacuum evacuation system comprises a combination of a mechanical booster provided on a vacuum side, which is a vacuum pump of Roots blower type, and an oil-sealed rotary vacuum pump provided on an atmospheric side. In addition, U.S. Pat. No. 3,969,039 discloses another conventional vacuum evacuation system in which axial flow turbomolecular pumping means, centrifugal compressor means and fluid diode pumping means are arranged on a single shaft in side-by-side relation so as to be connected to each other.
The former system has such problems that, since a working chamber of the oil-sealed rotary vacuum pump is filled with oil, back-diffusion of the oil to the vacuum-side occurs, and since the pumping speed of the mechanical booster decreases from about 10.sup.-2 Torr, the system is unsuitable for an evacuation system for semiconductor manufacturing apparatuses and the like, which requires particularly high cleanness and high pumping speed in high vacuum.
The latter system has such a problem that, since various kinds of pumping means are connected to each other by the single shaft, it is impossible to drive the pumping means at revolution speeds or rotational speeds respectively suitable for the pumping means.